Characterization of the artificial haptic perception neurons. a) The circuit diagram of the haptic perception neuron. b) IV curves of the piezoresistive sensor with different applied pressures/weights. c) The output resistance of sensor as a function of weight. The solid line is fitting result by Equation (3). d) Neuronal response of the haptic perception neuron under a constant bias voltage (5 V, 20 μs) and the influence of varying pressure. The output frequencies are 0.45, 0.55, 0.75, and 0.95 MHz at the pressures/weights of 100, 150, 200, and 250 g, respectively e) Recognition of braille characters (“p”, “k”, “u”) using tactile sensing. Without convex patterns (that is, two sensors have no pressure), the output frequency is zero. With convex patterns both on the left and right (that is, two sensors both have pressure by applying 100 g), the output frequency is ~1.1 MHz. With convex patterns only on one of the left and right (that is, the only one of two sensors has pressure), the output frequency is ~0.4 MHz.